1. Field of the Invention
The present invention relates generally to a planar antenna module for a millimeter-wave radar system for use on motor vehicles. More particularly, it relates to a planar antenna module which is capable of integrating a plurality of planar antenna elements and a plurality of circulators in a limited mounting or packaging space and which is suitable for a motor vehicle millimeter-wave radar system for wide scanning angular range and high bearing resolution.
2. Description of the Related Art
The present inventors have proposed "a radar module and an antenna device" for an FM millimeter-wave radar system for use on motor vehicles, as described in the co-pending U.S. patent application Ser. No. 08/611,665 and European Patent Application No. 96104536.6.
The motor vehicle millimeter-wave radar system includes an offset defocused parabolic antenna composed of a primary radiator of a deafest multiple-beam antenna including planar array antenna elements, and a secondary radiator having a parabolic reflecting surface. Electromagnetic waves in a millimeter wavelength range which are radiated from the planar array antenna elements of transmitting and receiving channels are radiated by the secondary reflector at respective different angles or bearings in a horizontal direction forwardly of a motor vehicle. Some of the electromagnetic waves are reflected by objects, travel back along the reverse course of the radiation, and are received by the planar array antenna elements for subsequent signal processing operation by which distances to the objects which have produced the reflected waves in the respective transmitting and receiving channels (bearings) are calculated to make up a two-dimensional map of obstacles in the forward direction of the motor vehicle.
FIG. 7 shows the structure of the "FM radar module" described in the specification of the co-pending applications specified above.
In FIG. 7, the FM radar module 50 includes MMICs (monolithic microwave integrated circuits) 53A-53H, circulators 54A-54P for separating signals to be transmitted and signals received, and planar array antenna elements 52A-52P, all the components being provided on a common dielectric substrate 51.
The MMICs 53A-53H each include a transmitting portion and a receiving portion on a single semiconductor substrate. The respective transmitting portions amplify high-frequency signals supply the respective planar array antenna elements 52A-52P with transmitted signals. Each of the receiving portion is provided with an amplifier for amplifying a local signal, and a mixer for mixing the amplified local signal with a signal received by a corresponding one of the planar array antenna elements 52A-52P.
The antenna assembly 52 is composed of a plurality of rectangular patches spaced a predetermined distance. The planar array antenna elements 52A-52P each corresponding to one of a plurality of transmitting and receiving channels are divided into two groups. The planar array antenna elements 52A-52H of one group and the planar array antenna elements 52I-52P of the other group are arranged in interdigitating pattern and extend in opposite directions that are 180 degrees apart from each other.
In the motor vehicle millimeter-wave radar system, the resolution in a horizontal direction of the two-dimensional map is determined by the number of planar antenna elements employed for transmitting and receiving electromagnetic waves. Accordingly, in order to generate a high-resolution two-dimensional map, a greater number of planar antenna elements and circulators should be integrated on the dielectric substrate.